1. Field of the Invention
A toroidal type continuously variable transmission and A continuously variable transmission apparatus according to the present invention are each utilized as a transmission unit constituting an automatic transmission for an automobile. In particular, the invention intends to suppress the variation of the transmission ratio based on the elastic deformation of a trunnion even under a state that a toque to be transmitted changes abruptly thereby to reduce uncomfortable feeling of a driver.
2. Description of the Related Art
A toroidal type continuously variable transmission as shown schematically in FIGS. 12 to 13 has been partially utilized as an automatic transmission for an automobile. This toroidal type continuously variable transmission is configured in a manner as disclosed in Japanese Patent Laid-Open No. 71465/1988, for example, that an input side disk 2 is supported concentrically with an input shaft 1 and an output side disk 4 is fixed at the end portion of an output shaft 3 disposed concentrically with the input shaft 1. Trunnions 7, 7, which swing around pivot shafts 6, 6 disposed at twisted positions with respect to the input shaft 1 and the output shaft 3, respectively, are provided at the inner side of a casing 5 (see FIGS. 15 to 16 described later) in which the toroidal type continuously variable transmission is housed.
A pair of the pivot shafts 6, 6 are provided concentrically at the outer surfaces of the both ends of each of the trunnions 7, 7. The center axis of each of the pivot shafts 6, 6 exists at the twisted position which does not cross with the center axes of the respective disks 2, 4 but is perpendicular to or almost perpendicular to the direction along the center axes of the respective disks 2, 4. The base half portions of displacement shafts 8, 8 are supported by the center portions of the trunnions 7, 7 so that the slanted angle of each of the displacement shafts 8, 8 is freely adjustable by swinging the trunnions 7, 7 around the pivot shafts 6, 6, respectively. Power rollers 9, 9 are rotatably supported at the peripheries of the tip half portions of the displacement shafts 8, 8 supported by the trunnions 7, 7, respectively. Each of the power rollers 9, 9 is sandwiched between the inner surfaces 2a, 4a of the input and output side disks 2, 4.
Each of the opposing inner surfaces 2a, 4a of the input and output side disks 2, 4 is configured as a concave surface of an arc shape in its section which is obtained by rotating an arc formed around the pivot shaft 6 as a center or by rotating a curve close to such an arc. The peripheral surfaces 9a, 9a of the power rollers 9, 9 each formed in a spherical convex surface contact against the inner surfaces 2a, 4a. A pressing device 10 such as a loading cam device etc. is provided between the input shaft 1 and the input side disk 2. The pressing device 10 elastically pushes the input side disk 2 toward the output side disk 4 thereby to freely rotate and drive the output side disk 4.
At the time of using the toroidal type continuously variable transmission configured in the aforesaid manner, the pressing device 10 rotates the input side disk 2 in accordance with the rotation of the input shaft 1 while pressing the input side disk 2 toward the plurality of the power rollers 9, 9. The rotation of the input side disk 2 is transmitted to the output side disk 4 through the plurality of the power rollers 9, 9, whereby the output shaft 3 fixed to the output side disk 4 rotates.
A description will be given of the case of changing the rotation speed between the input shaft 1 and the output shaft 3. First, at the time of performing the deceleration between the input shaft 1 and the output shaft 3, the trunnions 7, 7 are swung around the pivot shafts 6, 6 thereby to incline the displacement shafts 8, 8 such that the peripheral surfaces 9a, 9a of the power rollers 9, 9 contact against the center side portion of the inner surface 2a of the input side disk 2 and the outer peripheral side portion of the inner surface 4a of the output side disk 4 as shown in FIG. 12, respectively.
In contrast, at the time of increasing the speed, the trunnions 7, 7 are swung thereby to incline the displacement shafts 8, 8 such that the peripheral surfaces 9a, 9a of the power rollers 9, 9 contact against the outer peripheral side portion of the inner surface 2a of the input side disk 2 and the center side portion of the inner surface 4a of the output side disk 4 as shown in FIG. 13, respectively. When the inclined angle of each of the displacement shafts 8, 8 is set at the intermediate angle between those in FIGS. 12 and 13, an intermediate transmission gear ratio can be obtained between the input shaft 1 and the output shaft 3.
Further, FIGS. 14 to 15 show a further specific toroidal type continuously variable transmission described in Japanese Patent Laid-Open No. 173552/1989. An input side disk 2 and an output side disk 4 are rotatably supported at the periphery of a tubular input shaft 11. A pressing device 10 is provided between the end portion of the input shaft 11 and the input side disk 2. An output gear 12 is coupled to the output side disk 4 so that the output side disk 4 and the output gear 12 rotate synchronously.
Pivot shafts 6, 6 provided concentrically at the both end portions of the pair of trunnions 7, 7 are supported by a pair of supporting plates (yokes) 13, 13, respectively, so as to swing and displace freely in the axial direction (the front and rear direction in FIG. 14, the vertical direction in FIG. 15). The base half portions of displacement shafts 8, 8 are supported by the intermediate portions of the trunnions 7, 7, respectively. Each of the displacement shafts 8, 8 is configured in a manner that the base half portion and the tip half portion thereof are made eccentric to each other. The base half portions are rotatably supported by the intermediate portions of the trunnions 7, 7 and power rollers 9, 9 are rotatably supported by the tip half portions, respectively. A synchronous cable 27 is hung over the end portions of the trunnions 7, 7 in a sleeve tied manner so that the inclined angles of the respective trunnions 7, 7 are mechanically synchronized to each other.
The pair of the displacement shafts 8, 8 are provided at opposite side positions with respect to the input shaft 11 so as to form 180 degrees therebetween. The base half portion and the tip half portion of each of the displacement shafts 8, 8 are made eccentric in the same direction (vertically reverse direction in FIG. 15) with respect to the rotation direction of the input and output side disks 2, 4. The eccentric direction is made almost perpendicular to the direction along which the input shaft 11 is disposed. Thus, the power rollers 9, 9 are supported so as to be able to slightly displace freely with respect to the disposing direction of the input shaft 11.
From the outer periphery sides of the power rollers 9, 9, thrust ball bearings 14, 14 and thrust needle roller bearings 15, 15 are sequentially provided between the outer peripheries of the power rollers 9, 9 and the inner side surfaces at the intermediate portions of the trunnions 7, 7. The thrust ball bearings 14, 14 allow the power rollers 9, 9 to rotate while supporting the load in the thrust direction applied to the power rollers 9, 9, respectively. The thrust needle roller bearings 15, 15 allow the tip half portions of the displacement shafts 8, 8 and the outer rings 16, 16 to swing around the base half portions of the displacement shafts 8, 8 while supporting the thrust load applied to the outer rings 16, 16 constituting the thrust ball bearings 14, 14 from the power rollers 9, 9, respectively. Further, the trunnions 7, 7 can be displaced freely in the axial direction of the pivot shafts 6, 6 by hydraulic type actuators (hydraulic cylinder) 17, 17, respectively.
In the toroidal type continuously variable transmission configured in the aforesaid manner, the rotation of the input shaft 11 is transmitted to the input side disk 2 through the pressing device 10. Then, the rotation of the input side disk 2 is transmitted to the output side disk 4 through the pair of the power rollers 9, 9 and the rotation of the output side disk 4 is taken out by an output gear 12.
In the case of changing a rotation speed ratio between the input shaft 11 and the output gear 12, the pair of the trunnions 7, 7 are made swing in opposite directions to each other by the actuators 17, 17, respectively. For example, the power roller 9 on the right side in FIG. 15 is displaced to the lower side in the figure, whilst the power roller 9 on the left side in the figure is displaced to the upper side in the figure. As a result, the directions of forces along the tangential directions acting on the contact portions between the peripheral surfaces 9a, 9a of the power rollers 9, 9 and the inner surfaces 2a, 4a of the input side disk 2 and the output side disk 4 change (that is, sideslip occurs at the contact portions), respectively. Then, due to the change of the direction of the force, the trunnions 7, 7 swing in opposite directions to each other around the pivot shafts 6, 6 pivotally supported by supporting plates 13, 13, respectively. As a result, as shown in FIGS. 12 to 13, the contact positions between the peripheral surfaces 9a, 9a of the power rollers 9, 9 and the inner surfaces 2a, 4a change, and thus the rotation speed ratio between the input shaft 11 and the output gear 12 changes.
The pressure oil is supplied to and discharged from the actuators 17, 17 by means of a single control valve irrespective of the number of the actuators 17, 17. The movement of one of the trunnions 7 is fed back to the control valve. The structure of this portion is conventionally known as disclosed in U.S. Pat. No. 5,464,375 and will be explained briefly with reference to FIG. 18 which shows the second example of the conventional specific structures described later. The control valve 18 includes a sleeve 20 which is displaced in the axial direction thereof (left and right directions in FIG. 18) by a stepping motor 19 and a spool 21 fitted into the inner diameter side of the sleeve 20 so as to displace freely in the axial direction thereof. A precess cam 23 is fixed at the end portion of a rod 22 attached to one of the trunnions 7. A feedback mechanism is configured in a manner that the movement of the rod 22 is transmitted to the spool 21 through the precess cam 23 and a link arm 24.
At the time of switching the transmission state, the sleeve 20 is displaced by a predetermined amount by the stepping motor 19 to open the flow path of the control valve 18. As a result, the pressure oil is supplied in predetermined direction to the actuators 17, 17, whereby the actuators 17, 17 displace the trunnions 7, 7 in a predetermined direction, respectively. That is, in accordance with the supply of the pressure oil, the trunnions 7, 7 swing around the pivot shafts 6, 6 while displacing in the axial direction of the pivot shafts 6, 6, respectively. Then, the movement (the displacement in the axial direction and the swinging movement) of one of the trunnions 7 is transmitted to the spool 21 through the precess cam 23 fixed to the end portion of the rod 22 and the link arm 24 thereby to displace the spool 21 in the axial direction. As a result, the flow path of the control valve 18 is closed in a state that the trunnions 7 are displaced by the predetermined amount, so that the supply and discharge of the pressure oil to and from the actuators 17, 17 is stopped. Thus, the displacement amount of the trunnions 7, 7 in the axial direction and the swinging direction corresponds to an amount merely according to the displacement amount of the sleeve 20 caused by the stepping motor 19.
Incidentally, at the time of power transmission by the toroidal type continuously variable transmission, the power rollers 9, 9 displace in the axial direction of the input shaft 11 (FIGS. 14 to 15) based on the elastic deformation of the respective portions of the transmission. Then, the displacement shafts 8, 8 supporting the power rollers 9, 9 slightly rotate around the base half portions thereof, respectively. As a result of the rotation, the outer surfaces of the outer rings 16, 16 of the thrust ball bearings 14, 14 and the inner surfaces of the trunnions 7, 7 displace relative to each other. A force required for the relative displacement is small since the thrust needle roller bearings 15, 15 exist between the outer surfaces and the inner surfaces.
Further, a so-called double cavity type structure has been known conventionally in which, in order to increase transmissible torque, as shown in FIGS. 16 to 18, two input side disks 2A, 2B and two output side disks 4, 4 are provided at the periphery of an input shaft 11a, and these two input side disks 2A, 2B and the two output side disks 4, 4 are juxtaposed to each other with respect to the power transmission direction. The structure shown in FIGS. 16 to 18 is configured in a manner that an output gear 12a is supported at the periphery of the intermediate portion of the input shaft 11a so as to rotate freely with respect to the input shaft 11a, and the output side disks 4, 4 are spline-engaged at the both end portions of a cylindrical portion provided at the center portion of the output gear 12a. The input side disks 2A, 2B are supported at the both end portions of the input shaft 11a so as to rotate together with the input shaft 11a. The input shaft 11a is driven and rotated by a driving shaft 25 through a loading cam type pressing device 10.
In the double cavity type toroidal type continuously variable transmission configured in the aforesaid manner, the power transmission from the input shaft 11a to the output gear 12a is performed by two ways separately, that is, one way is between the one input side disk 2A and the output side disk 4 and the other way is between the other input side disk 2B and the output side disk 4, so that a large torque can be transmitted. Also, according to such a double cavity type toroidal type continuously variable transmission, at the time of transmission, hydraulic type actuators 17, 17 displace trunnions 7, 7 in the axial direction of the pivot shafts 6, 6, respectively. As described above, in order to control the supply and the discharge of the pressure oil to and from the actuators 17, 17 for performing the transmission, only one control valve 18 is provided for the toroidal type continuously variable transmission. This only one control valve 18 is used to control the supply and the discharge of the pressure oil to and from the plurality of the actuators 17, 17.
It has been proposed conventionally as disclosed in Japanese Patent Laid-Open No. 169169/1989, Japanese Patent Laid-Open No. 312266/1989, U.S. Pat. No. 5,888,160, U.S. Pat. 6,171,210 etc. that, in the case of incorporating the toroidal type continuously variable transmission configured and operated in the aforesaid manner into an actual continuously variable transmission for an automobile, the transmission is combined with a planetary gear mechanism thereby to constitute a continuously variable transmission apparatus. A so-called power split type continuously variable transmission apparatus of such transmission apparatuses is configured in a manner that the driving force of an engine is transmitted only by a toroidal type continuously variable transmission at the time of low speed running, whilst the driving force is transmitted by a planetary gear mechanism at the time of high speed running thereby to reduce torque applied to the toroidal type continuously variable transmission at the time of the high speed running. According to such a configuration, it is possible to improve the durability of the respective constituent members of the toroidal type continuously variable transmission. Alternately, a so-called geared neutral continuously variable transmission has been conventionally known in which it makes possible to stop an output shaft while rotating an input shaft by combining a toroidal type continuously variable transmission and a planetary gear mechanism.
FIG. 19 shows the continuously variable transmission disclosed in U.S. Pat. No. 5,888,160. This continuously variable transmission is provided with a starter clutch 30 between the output side terminal portion (the right end portion in FIG. 19) of a crankshaft 28 of an engine 26 and the input side end portion (the left end portion in FIG. 19) of an input shaft 29. An output shaft 31 for taking out power based on the rotation of the input shaft 29 is disposed in parallel to the input shaft 29. A toroidal type continuously variable transmission 32 is provided at the periphery of the input shaft 29 and a planetary gear mechanism 33 is provided at the periphery of the output shaft 31.
A cam plate 34 constituting the pressing device 10 of the toroidal type continuously variable transmission 32 is fixed at a portion close to the output side end portion (to the right in FIG. 19) of the intermediate portion of the input shaft 29. The input side disk 2 and the output side disk 4 are supported by bearings (not-shown) such as a needle roller bearing etc. at the periphery of the input shaft 29 so as to rotate freely and independently to each other with respect to the input shaft 29. The cam plate 34 and the input side disk 2 constitute the pressing device 10. Thus, the input side disk 2 rotates in accordance with the rotation of the input shaft 29 while being pressed toward the output side disk 4. A plurality of power rollers 9, 9 are sandwiched between the inner surface 2a of the input side disk 2 and the inner surface 4a of the output side disk 4, whereby the toroidal type continuously variable transmission 32 as shown in FIGS. 14 to 15 is constituted. The toroidal type continuously variable transmission 32 is not limited to the single cavity type shown in FIG. 19 and FIGS. 14 to 15 but may be the double cavity type shown in FIGS. 16 to 17. The continuously variable transmission apparatus in which the double cavity type toroidal type continuously variable transmission is incorporated is disclosed in U.S. Pat. No. 6,171,210 etc.
A sun gear 35 constituting the planetary gear mechanism 33 is fixed to the input side end portion (the right end portion in FIG. 19) of the output shaft 31. Thus, the output shaft 31 rotates in accordance with the rotation of the sun gear 35. A ring gear 36 is supported at the periphery of the sun gear 35 so as to be concentric with the sun gear 35 and rotate freely. A plurality of (normally three or four) planetary gear sets 37, 37 are provided between the inner peripheral surface of the ring gear 36 and the outer peripheral surface of the sun gear 35. In the example shown by the figure, each of the planetary gear sets 37, 37 is formed by combining a pair of planetary gears 38a, 38b. The pair of the planetary gears 38a, 38b mesh to each other. Further, the planetary gear 38a disposed on the outer diameter side is meshed with the ring gear 36, and the planetary gear 38b disposed on the inner diameter side is meshed with the sun gear 35. Each of the planetary gear sets 37, 37 is formed by the pair of the planetary gears 38a, 38b in this manner in order to coincide the rotation direction of the ring gear 36 with that of the sun gear 35. Thus, if it is not necessary to coincide the rotation direction of the ring gear 36 with that of the sun gear 35 in relation to other constituent portions, a single planetary gear may be arranged to mesh with both the ring gear 36 and the sun gear 35. The planetary gear sets 37, 37 are supported at the one side surface (the right side surface in FIG. 19) of a carrier 39 so as to rotate freely. The carrier 39 is supported at the intermediate portion of the output shaft 31 so as to rotate freely.
The carrier 39 and the output side disk 4 are coupled in a state of being capable of transmitting rotation force by a first power transmission mechanism 40. The first power transmission mechanism 40 constituting a first power transmission path is formed by first and second gears 41, 42 meshed to each other. Thus, the carrier 39 rotates at a speed according to the numbers of the gear teeth of the first and second gears 41, 42 in accordance with the rotation of the output side disk 4 in the direction opposite to the rotation direction of the output side disk 4.
The input shaft 29 and the ring gear 36 are coupled freely in a state of being capable of transmitting rotation force by a second power transmission mechanism 43. The second power transmission mechanism 43 constituting a second power transmission path is formed by first and second sprockets 44, 45 and a chain 46 hung over the both sprockets 44, 45. That is, the first sprocket 44 is fixed at a portion protruding from the cam plate 34 at the output side end portion (the right end portion in FIG. 19) of the input shaft 29 and the second sprocket 45 is fixed at the input side end portion (the right end portion in FIG. 19) of a transmission shaft 47. Thus, the transmission shaft 47 rotates at a speed according to the numbers of the gear teeth of the first and second sprockets 44, 45 in accordance with the rotation of the input shaft 29 in the same direction as the rotation direction of the input shaft 29.
The continuously variable transmission apparatus includes a clutch mechanism constituting a mode switching device. The clutch mechanism couples only one of the carrier 39 and the transmission shaft 47 that is a constituent member of the second power transmission mechanism 43 to the ring gear 36. In the case of the construction shown in FIG. 19, the clutch mechanism is formed by a low speed clutch 48 and a high speed clutch 49. The low speed clutch 48 is provided between the outer peripheral edge portion of the carrier 39 and the one end portion (the left end portion in FIG. 19) of the ring gear 36 along the axial direction thereof. Such a low speed clutch 48 serves at the time of coupling to prevent the relative displacement among the sun gear 35, the ring gear 36 and the planetary gear sets 37, 37 constituting the planetary gear mechanism 33 to integrally couple the sun gear 35 and the ring gear 36. The high speed clutch 49 is provided between the transmission shaft 47 and a center shaft 51 which is fixed to the ring gear 36 through a supporting plate 50. The low speed clutch 48 and the high speed clutch 49 are arranged in a manner that when one of these clutches is engaged, the other clutch is disengaged.
In the example shown in FIG. 19, a reverse clutch 52 is provided between the ring gear 36 and a fixed portion such as the housing (not shown) of the continuously variable transmission apparatus. The reverse clutch 52 is provided in order to rotate the output shaft 31 in the reverse direction so as to move an automobile backward. The reverse clutch 52 is disengaged in a state where one of the low speed clutch 48 and the high speed clutch 49 is engaged. In a state where the reverse clutch 52 is engaged, each of the low speed clutch 48 and the high speed clutch 49 is disengaged.
Further, in the example shown in the figure, the output shaft 31 and a differential gear 53 are coupled by a third power transmission mechanism 57 constituted by third to fifth gears 54 to 56. Thus, when the output shaft 31 rotates, a pair of left and right driving shafts 58, 58 rotate through the third power transmission mechanism 57 and the differential gear 53 thereby to rotate and drive the driving wheels of an automobile.
At the time of the low speed running, the continuously variable transmission apparatus first engages the low speed clutch 48 and disengages the high speed clutch 49 and the reverse clutch 52. When the starter clutch 30 is engaged to rotate the input shaft 29 in this state, only the toroidal type continuously variable transmission 32 transmits the power from the input shaft 29 to the output shaft 31. The operation for changing the transmission ratio (variable speed ratio) between the input side disk 2 and the output side disk 4 at the time of such a low speed running is same as that in the case of using only the toroidal type continuously variable transmission as shown in FIGS. 14 to 15. Of course, in this state, the transmission ratio between the input shaft 29 and the output shaft 31, that is the transmission ratio of the entirety of the continuously variable transmission apparatus is proportional to the transmission ratio of the toroidal type continuously variable transmission 32. Further, in this state, a torque inputted into the toroidal type continuously variable transmission 32 becomes equal to a torque applied to the input shaft 29.
In contrast, at the time of the high speed running, the high speed clutch 49 is engaged and each of the low speed clutch 48 and the reverse clutch 52 is disengaged. When the starter clutch 30 is engaged to rotate the input shaft 29 in this state, the first and second sprockets 44, 45 and the chain 46 constituting the second power transmission mechanism 43 and the planetary gear mechanism 33 transmit the power from the input shaft 29 to the output shaft 31.
That is, when the input shaft 29 rotates at the time of the high speed running, this rotation is transmitted to the center shaft 51 through the second power transmission mechanism 43 and the high speed clutch 49 thereby to rotate the ring gear 36 to which the center shaft 51 is fixed. Then, the rotation of the ring gear 36 is transmitted to the sun gear 35 through the plurality of the planetary gear sets 37, 37 thereby to rotate the output shaft 31 to which the sun gear 35 is fixed. When the ring gear 36 is disposed on the input side, the planetary gear mechanism 33 increases the speed at the transmission ratio according to the numbers of the gear teeth between the ring gear 36 and the sun gear 35 supposing that the planetary gear sets 37, 37 are stopped (not revolve around the sun gear 35). In this respect, each of the planetary gear sets 37, 37 revolve around the sun gear 35, and the transmission ratio of the entirety of the continuously variable transmission apparatus changes in accordance with the revolution speed of the planetary gear sets 37, 37. Thus, the transmission ratio of the entirety of the continuously variable transmission apparatus can be adjusted by changing the transmission ratio of the toroidal type continuously variable transmission 32 and changing the revolution speed of the planetary gear sets 37, 37.
That is, at the time of the high speed running, the planetary gear sets 37, 37 revolve in the same direction as the ring gear 36. The lower the revolution speed of each of the planetary gear sets 37, 37 become, the higher the rotation speed of the output shaft 31 to which the sun gear 35 is fixed becomes. For example, when the revolution speed becomes same as the rotation speed of the ring gear 36 (each being an angular velocity), the rotation speed of the ring gear 36 becomes same as that of the output shaft 31. When the revolution speed is lower than the rotation speed of the ring gear 36, the rotation speed of the output shaft 31 becomes higher than that of the ring gear 36. On the contrary, when the revolution speed is higher than the rotation speed of the ring gear 36, the rotation speed of the output shaft 31 becomes lower than that of the ring gear 36.
Thus, at the time of the high speed running, as the transmission ratio of the toroidal type continuously variable transmission 32 is changed to the deceleration side, the transmission ratio of the entirety of the continuously variable transmission apparatus changes to the speed increasing side. In such a high speed running state, a torque is applied to the toroidal type continuously variable transmission 32 not from the input side disk 2 but from the output side disk 4 (that is, a minus torque is applied supposing that a torque applied at the time of the low speed running is plus torque). That is, in the state where the high speed clutch 49 is engaged, a torque transmitted to the input shaft 29 from the engine 26 is transmitted to the ring gear 36 of the planetary gear mechanism 33 through the second power transmission mechanism 43 before the pressing device 10 presses the input side disk 2. Therefore, a torque is scarcely transmitted to the input side disk 2 from the input shaft 29 side through the pressing device 10.
A part of a torque transmitted to the ring gear 36 of the planetary gear mechanism 33 through the second power transmission mechanism 43 is transmitted to the output side disk 4 from the planetary gear sets 37, 37 through the carrier 39 and the first power transmission mechanism 40. In this manner, a torque applied to the toroidal type continuously variable transmission 32 from the output side disk 4 becomes smaller as the transmission ratio of the toroidal type continuously variable transmission 32 is changed to the deceleration side in order to change the transmission ratio of the entirety of the continuously variable transmission apparatus to the speed increasing side. As a result, a torque inputted into the toroidal type continuously variable transmission 32 can be made small at the time of the high speed running thereby to improve the durability of the constituent parts of the transmission 32.
Further, at the time of rotating the output shaft 31 reversely so as to move an automobile backward, each of the low speed clutch 48 and the high speed clutch 49 is disengaged and also the reverse clutch 52 is engaged. As a result, the ring gear 36 is fixed, and the planetary gear sets 37, 37 revolve around the sun gear 35 while being meshed with the ring gear 36 and the sun gear 35. Then, the sun gear 35 and the output shaft 31 fixing the sun gear 35 thereto rotate in the direction opposite to the rotation direction thereof at the time of the low speed running and the high speed running.
FIG. 20 shows an example of a state where the transmission ratio (icvt) of the toroidal type continuously variable transmission 32, an input torque (Tin) inputted into the toroidal type continuously variable transmission 32 and an output torque (Ts) taken out from the output shaft of the continuously variable transmission change in the case of continuously changing the transmission ratio (itotal) of the entirety of the continuously variable transmission apparatus as shown in FIG. 19. The relation among the respective transmission ratios (itotal), (icvt) and the respective torques (Tin) (Ts) changes depending on the variable speed width of the toroidal type continuously variable transmission 32, the construction and gear teeth ratio of the planetary gear mechanism 33, the deceleration ratio of the mechanism 43 etc. In order to obtain the respective lines shown in FIG. 20, the following conditions are determined that the variable speed width of the transmission 32 is set to four times (0.5 to 2.0), the planetary gear mechanism 33 includes the planetary gear sets 37, 37 each formed by the pair of the planetary gears 38a, 38b, and the deceleration ratio of the second power transmission mechanism 43 is 2. The switching between the low speed clutch 48 and the high speed clutch 49 is performed when the transmission ratio (itotal) of the entirety of the continuously variable transmission apparatus is 1.
In FIG. 20 showing the result of the provisional calculation based on the aforesaid conditions, an ordinate represents the transmission ratio (icvt) of the toroidal type continuously variable transmission 32 and the ratio (Tin/Te; Ts/Te) between the input torque (Tin) of the toroidal type continuously variable transmission 32 or the output torque (Ts) of the continuously variable transmission apparatus and the torque (Te) transmitted to the input shaft 29 (FIG. 19) from the engine 26, and an abscissa represents the transmission ratio (itotal) of the entirety of the continuously variable transmission apparatus. In this respect, a value representing the transmission ratio (icvt) of the toroidal type continuously variable transmission 32 is minus since the rotation direction of the output side disk 4 (FIG. 19) incorporated into the transmission 32 is in opposite to that of the input shaft 29. A solid line a represents the transmission ratio (icvt) of the toroidal type continuously variable transmission 32, a broken line b represents a ratio (Ts/Te) between the output torque (Ts) and the torque (Te) transmitted to the input shaft 29 from the engine 26, and a chain line c represents a ratio (Tin/Te) between the input torque (Tin) and the torque (Te) transmitted to the input shaft 29 from the engine 26. As clear from such a FIG. 20, according to the continuously variable transmission apparatus shown in FIG. 19, a torque applied to the transmission 32 at the time of the high speed running can be made small. According to the conditions for obtaining the result shown in FIG. 20, the input torque (Tin) can be reduced at the maximum to about 14% of the torque (Te) transmitted to the input shaft 29 from the engine 26.
The inventors of the present invention etc. have found the following matter from the experimentation. That is, according to the toroidal type continuously variable transmission configured in the aforesaid manner which is used in a state of being incorporated into the continuously variable transmission apparatus etc. configured in the aforesaid manner, irrespective of the opening and closing control of the control valve 18 (FIG. 18) by the precess cam 23, the transmission ratio varies unnecessarily in accordance with the variation of the input torque due to the influence of a clearance(s) of the assembled parts and the elastic deformation of the constituent parts of the mechanism 32 and so the rotational speed of the engine varies abruptly, so that a driver may feel uncomfortable feeling. It was found that, in particular, the unnecessary variation of the transmission ratio becomes remarkable when the torque transmitted through the toroidal type continuously variable transmission varies.
That is, according to the experimentation performed by the inventors of the present invention, it was found that when the torque transmitted through the toroidal type continuously variable transmission varies, the transmission ratio of the toroidal type continuously variable transmission changes despite that no command for the transmission is issued. FIG. 21 shows the result of such an experimentation. The experimentation has been performed in a state that the transmission ratio of the toroidal type continuously variable transmission is set to 1 (even speed), the rotation speed of the input shaft is set at 2000minxe2x88x921, and the temperature of the traction oil is increased like the actual running state of an automobile. Under the aforesaid condition, the torque applied to the input shaft was changed between xe2x88x92250Nxc2x7m and +350Nxc2x7m. The torque was changed gradually in order to exclude the influence of inertia as much as possible. In this respect, the negative state of the torque applied to the input shaft is a state where a torque is transmitted from the output side disk to the input side disk.
As clear from the result of the experimentation performed under such a condition, the transmission ratio of the toroidal type continuously variable transmission varies in accordance with the change of the torque transmitted by the toroidal type continuously variable transmission. The reason causing such a variation of the transmission ratio is considered as follows.
As shown in FIG. 18, the precess cam 23 is supported by and fixed to the tip end portion (the lower end portion of FIG. 18) of the rod 22 which base end portion (the upper end portion of FIG. 18) is coupled and fixed to one of the trunnions 7. At the time of operating the toroidal type continuously variable transmission, the trunnion 7 is applied with a large force from the power roller 9 which is supported by the inner surface side of the trunnion. This force mainly includes the following two kinds of forces {circle around (1)}, {circle around (2)}.
{circle around (1)} Forces applied in accordance with the power transmission from the contact portions (traction portions) between the peripheral surfaces 9a of the power roller 9 and the inner surfaces 2a of the input side disks 2, 2A, 2B, the inner surface 4a of the output side disk 4.
{circle around (2)} A thrust load pushing the power roller 9 to the inner surface of the trunnion 7 based on the pushing force by the pressing device 10 (for example, see FIGS. 16 to 17).
Each of these forces {circle around (1)} and {circle around (2)} becomes a cause for deviating the precess cam 23 from the normal position.
First, the explanation will be made with reference to FIGS. 22A to 22C as to the reason why the precess cam 23 deviates from the normal position due to the force {circle around (1)}. FIG. 22 schematically shows the pair of the trunnions 7, 7 disposed between the pair of the input side disk and the output side disk, the displacement shafts 8, 8, the power rollers 9, 9 and the rods 22, 22 respectively attached to the trunnions 7, 7, pistons 59, 59 constituting a hydraulic type actuator, and the precess cam 23. In FIG. 22, the input side disk not shown in FIG. 22 rotates clockwise as shown by an arrow xcex1. Thus, the output side disk also not shown in FIG. 22 rotates counterclockwise.
First, FIG. 22A shows a case where no power is transmitted between the input side disk 2 and the output side disk 4 (see FIG. 14, for example). In this case, a load applied to the power rollers 9, 9 from the inner surfaces 2a, 4a (see FIG. 14, for example) of the input side disk 2 and the output side disk 4 is zero. Thus, a load applied to the displacement shafts 8, 8 and the trunnions 7, 7 supporting the power rollers 9, 9 is also zero, so that each of the displacement shafts 8, 8 does not incline and each of the trunnions 7, 7 does not deform elastically. Therefore, the precess cam 23 fixed at the end portion of the rod 22 attached to one of the trunnions 7 (the right side one in FIG. 22) exists at the normal position shown by a chain line A in FIGS. 22A to 22C.
Next, FIG. 22B shows a case of transmitting a relatively small power between the input side disk 2 and the output side disk 4. In this case, loads along the axial direction (the vertical direction in FIG. 22) of the pivot shafts 6, 6 (see FIG. 18, for example) provided at the both end portions of the trunnions 7, 7 are applied to the trunnions 7, 7 based on the loads applied to the power rollers 9, 9 from the inner surfaces 2a, 4a of the input side disk 2 and the output side disk 4, respectively. Then, in order to support such loads, the oil is supplied to the actuators 17, 17 (see FIG. 18, for example) incorporating the pistons 59, 59, respectively. Simultaneously, as exaggeratingly shown in FIG. 22B, the displacement shafts 8, 8 supporting the power rollers 9, 9 incline in the direction to which the load applied to the power rollers 9, 9 from the input side disk 2 acts, based on the load applied to the power rollers 9, 9 from the both disks 2, 4, respectively. Such an inclination is based on the elastic deformation of the displacement shafts 8, 8 themselves and the presence of the inner clearance of a radial needle roller bearing provided between the both end portions of the displacement shafts 8, 8 and the power rollers 9, 9, the trunnions 7, 7, respectively. Although such an inclination is little, the inclination is caused by a relatively small force based on the presence of the inner clearances of the thrust ball bearing 14 and the thrust needle roller bearing 15 (see FIG. 18, for example) provided between the power rollers 9, 9 and the trunnions 7, 7, respectively.
When the displacement shafts 8, 8 incline in this manner, the power rollers 9, 9 supported by the displacement shafts 8, 8 displace with respect to the input side disk 2 and the output side disk 4, so that the positions of the contact portions (traction portions) between the peripheral surfaces 9a, 9a of the power rollers 9, 9 and the inner surfaces 2a, 4a of these both disks 2, 4 deviate from the center portions of these both disks 2, 4, respectively. When the traction portions deviate from the center portions of the both disks 2, 4, sideslip occurs at the traction portions between the peripheral surfaces 9a, 9a of the power rollers 9, 9 and the inner surfaces 2a, 4a of these both disks 2, 4. The known feedback mechanism operates based on the occurrence of such sideslip thereby to return the traction portions to the center portions of the both disks 2, 4. That is, the trunnions 7, 7 swingably displace around the pivot shafts 6, 6 together with the power rollers 9, 9 based on the sideslip, respectively, whereby the precess cam 23 displaces the spool 21 (see FIG. 18) of the control valve 18 through the link arm 24. Then, the pressure oil is supplied to and discharged from the actuators 17, 17 to displace the trunnions 7, 7 in the axial direction of the pivot shafts 6, 6 thereby to return the traction portions to the center portions of the both disks 2, 4, respectively. In this case, since an instruction signal for transmission is not delivered, the sleeve 20 (see FIG, 18) of the control valve 18 remains at the current position (does not displace in the axial direction). As a result, the power rollers 9, 9 perform the transmission operation despite that the instruction signal for transmission is not delivered. Then, the precess cam 23 exists at the position shown by the chain line B which is shifted by xcex41 in the axial direction from the normal position shown by the chain line A.
Further, FIG. 22C shows a case of transmitting a large power between the input side disk 2 and the output side disk 4. In this case, the force {circle around (2)} as well as the force {circle around (1)} acts to shift the precess cam 23 from the normal position.
That is, in this state shown by FIG. 22C, the slanted angle of the displacement shafts 8, 8 becomes larger than the case shown in FIG. 22B and also the elastic deformation of the trunnions 7, 7 increases to the non-negligible degree. In this case, the intermediate portions of the trunnions 7, 7 elastically deform based on the thrust loads applied from the power rollers 9, 9 in a direction that the inner surface sides of the intermediate portions of the trunnions at which the power rollers 9, 9 are provided form concave surfaces as exaggeratingly shown in FIG. 22C. The entire length of each of the trunnions 7, 7 relating to the axial direction of the pivot shafts 6, 6 becomes shorter based on the elastic deformation. To be more concrete, the both side surfaces of each of the trunnions along the longitudinal direction thereof displace in the direction approaching to the longitudinal center portion of each of the trunnions 7, 7.
As a result of the displacement, the precess cam 23 further shifts by xcex42 from the position shown by the chain line B as compared with the case shown in FIG. 22B. That is, in this state, the displacement amount of the precess cam 23 from the normal position shown by the chain line B becomes (xcex41+xcex42). Thus, the contact portions (traction portions) between the peripheral surfaces 9a, 9a of the power rollers 9, 9 and the inner surfaces 2a, 4a of these both disks 2, 4 deviate by the distance (xcex41+xcex42) from the center portions of these both disks 2, 4, respectively. As a result, the power rollers 9, 9 perform the transmission operation in accordance with the distance (xcex41+xcex42) despite that the instruction signal for transmission is not delivered. In this respect, the displacement xcex42 is sum of the displacement based on the elastic deformation of the trunnion 7 and the displacement based on the increase of the inclined angle of the displacement shaft 8.
In this manner in the cases shown in FIGS. 22B and 22C, the transmission operation is performed despite that the instruction signal for transmission is not delivered. The degree of the transmission in these cases is proportional to the axial displacement {xcex41 or (xcex41+xcex42)} and the cam lead of the precess cam 23. For example, in the case where the cam lead is 20 mm/360 degrees, when the aforesaid displacement is 0.3 mm, the power rollers 9, 9 rotate by 5.4 degrees (that is, swingably rotate around the pivot shafts 6, 6). Thus, it is important to suppress the displacement of the precess cam 23 to a small value in order to suppress the non-intentional transmission operation based on the aforesaid reason etc.
The non-intentional transmission operation is also generated by the swinging of the rod 22 based on the elastic deformation of the trunnion 7 at which the precess cam 23 is provided. Such a phenomenon will be explained with reference to FIG. 23. At the time of the power transmission, the trunnion 7 elastically deforms based on the thrust load applied from the power roller 9 supported by the inner surface of the trunnion in a direction that the inner surface side of the trunnion forms a concave surface as shown in FIG. 23 in which the center portion of the trunnion is shown by a thick chain line in an exaggeration manner. Then, the rod 22, which base end portion (the upper end portion in FIG. 23) is coupled and fixed to the end portion of the trunnion 7, displaces based on the elastic deformation. The more the thrust load becomes, the more the displacement amount relating the radial direction of the tip end portion (the lower end portion in FIG. 23) of the rod 22 at which the precess cam 23 is mounted becomes. Such displacement also becomes the cause of the aforesaid non-intentional transmission operation.
As clear from the aforesaid explanation, an amount of the displacement of the precess cam 23 from the normal position that is the cause of the non-intentional transmission operation changes in accordance with the magnitude of the force applied to the power roller 9. The magnitude of the force applied to the power roller 9 changes almost in proportional to the magnitude of the torque transmitted by the toroidal type continuously variable transmission. Thus, the transmission ratio of the toroidal type continuously variable transmission changes in accordance with the change of the torque even in a state where the signal for changing the transmission ratio is not delivered.
In any case, when the non-intentional transmission operation is performed, instantaneously the rotation speed of the engine changes abruptly, and so a driver feels uncomfortable feeling. Although it is difficult to completely eliminate such a non-intentional transmission operation, it is important to suppress the non-intentional transmission operation to a minimum degree in an aspect of performing the stable operation thereby not to apply uncomfortable feeling to a driver.
In particular, in the case of the continuously variable transmission apparatus configured by combining the toroidal type continuously variable transmission 32 and the planetary gear mechanism 33 as shown in FIG. 19, as clear from the right end side portion of the chain line c of FIG. 20, the transmission direction of the torque is reversed the moment the clutch is switched between the low speed clutch 48 and the high speed clutch 49. In such a construction, the unnecessary fluctuation of the transmission ratio accompanied by the change of the torque transmitted through the toroidal type continuously variable transmission 32 becomes large, and so uncomfortable feeling applied to a driver becomes likely remarkable. This matter will be explained with reference to FIGS. 24A to 24C.
It is supposed that a torque transmitted through the toroidal type continuously variable transmission is continuously changed from a positive value to a negative value as shown in FIG. 24A, and in this case the instruction signal for the transmission is not delivered as shown in of FIG. 24B (the sleeve 20 of the control valve 18 shown in FIG. 18 is not displaced). In this case, the transmission ratio of the toroidal type continuously variable transmission varies by the aforesaid forces {circle around (1)}, {circle around (2)} in correspondence with the aforesaid change of the torque as shown in FIG. 24C. In this respect, even if the torque changes linearly, the transmission ratio changes non-linearly.
In order to suppress the variation of the transmission ratio shown in FIG. 24C, it is considered to deliver the instruction signal for the transmission in correspondence with the change of the torque passing through the toroidal type continuously variable transmission as shown in FIGS. 25A to 25C (to displace the sleeve 20 of the control valve 18 shown in FIG. 18). That is, the instruction signal for the transmission is delivered as shown in FIG. 25B in correspondence with the change of the torque as shown in FIG. 25A. As a result, the variation of the transmission ratio of the toroidal type continuously variable transmission can be suppressed to a small degree as shown in FIG. 25C.
In this respect, as clear from the comparison between FIGS. 25A and 25C, since the changing direction of the torque does not coincide with the changing direction of the transmission ratio over the entire region of the changing. Thus, even when the instruction signal for the transmission is delivered merely in correspondence with the change of the torque, there is a case where it is difficult to sufficiently eliminate the unnecessary transmission. That is, even in the case where such control operations shown in FIGS. 25A and 25B are performed, the unnecessary change of the transmission ratio is still caused as shown in FIG. 25C based on the difference between the changing direction of the torque and the changing direction of the transmission ratio.
An object of the invention is performed so as to suppress an unintentional transmission operation to a smaller degree in view of the aforesaid circumstances.
To attain the object, according to a first aspect of the invention, there is provided a toroidal type continuously variable transmission comprising:
first and second disks each having a concave-shaped inner surface with an arc shape in section, the first and second disks being supported concentrically to be rotatable independently in a state that the inner surfaces thereof are opposed to each other;
a plurality of trunnions each swingably rotating around pivot shafts which are disposed at twisted positions with respect to a center shaft of the first and second disks;
displacement shafts each being supported by an intermediate portion of corresponding one of the trunnions in a state of protruding from an inner surface of the corresponding one of the trunnions;
power rollers each having a spherical convex-shaped periphery and disposed on an inner surface side of corresponding one of the trunnions, each of the power rollers being supported around a periphery of corresponding one of the displacement shafts to be rotatable in a state of being sandwiched between the first and second disks;
a pressing device which presses the first disk toward the second disk, the pressing device generating a first pressing force corresponding to a magnitude of a torque transmitted between the first and second disks and a second pressing force independent from the torque; and
a controller controlling the pressing device to generate the second pressing force in accordance with a signal, wherein, when a magnitude of a torque transmitted between the first and second disks varies, the controller controls the pressing device to continuously generate a predetermined pressing force equal to or more than a pressing force necessary for transmitting a larger torque before and after the variation during the variation.
Further, according to a second aspect of the invention, in the toroidal type continuously variable transmission according to the first aspect, the pressing device is a hydraulic type actuator which generates a pressing force according to a hydraulic pressure in accordance with supply of pressure oil.
Moreover, according to a third aspect of the invention, there is provided a continuously variable transmission apparatus comprising:
an input shaft coupled to a driving source and driven and rotated by the driving source;
an output shaft for taking out a power based on the rotation of the input shaft;
a toroidal type continuously variable transmission;
a planetary gear mechanism;
a first power transmission path for transmitting a power inputted into the input shaft through the toroidal type continuously variable transmission;
a second power transmission path for transmitting the power inputted into the input shaft without passing through the toroidal type continuously variable transmission; and
a mode switching device for switching a state where the power inputted into the input shaft is transmitted to the planetary gear mechanism through the first power transmission path and the second power transmission path,
wherein the toroidal type continuously variable transmission includes:
first and second disks each having a concave-shaped inner surface with an arc shape in section, the first and second disks being supported concentrically to be rotatable independently in a state that the inner surfaces thereof are opposed to each other;
a plurality of trunnions each swingably rotating around pivot shafts which are disposed at twisted positions with respect to a center shaft of the first and second disks;
displacement shafts each being supported by an intermediate portion of corresponding one of the trunnions in a state of protruding from an inner surface of the corresponding one of the trunnions;
power rollers each having a spherical convex-shaped periphery and disposed on an inner surface side of corresponding one of the trunnions, each of the power rollers being supported around a periphery of corresponding one of the displacement shafts to be rotatable in a state of being sandwiched between the first and second disks;
a pressing device which presses the first disk toward the second disk, the pressing device generating a first pressing force corresponding to a magnitude of a torque transmitted between the first and second disks and a second pressing force independent from the torque; and
a controller controlling the pressing device to generate the second pressing force in accordance with a signal, wherein, when a magnitude of a torque transmitted between the first and second disks varies, the controller controls the pressing device to continuously generate a predetermined pressing force equal to or more than a pressing force necessary for transmitting a larger torque before and after the variation during the variation,
wherein the planetary gear mechanism includes:
a sun gear;
a ring gear disposed at periphery of the sun gear;
a planetary gear provided between the sun gear and the ring gear; and
a carrier for rotatably supporting the planetary gear,
wherein a power transmitted through the first power transmission path and a power transmitted through the second power transmission path is freely transmitted to two of the sun gear, the ring gear and the carrier, and remaining one of the sun gear, the ring gear and the carrier is coupled to the output shaft,
wherein the mode switching device switches at least between a first mode for transmitting power only through the first power transmission path and a second mode for transmitting power through both the first power transmission path and the second power transmission path, and
wherein the controller of the toroidal type continuously variable transmission controls the pressing device, during the switching of the mode switching device between the first mode and the second mode, to continuously generate a predetermined pressing force equal to or more than a pressing force necessary for transmitting a larger torque before and after the switching.
In addition, according to a fourth aspect of the invention, in the continuously variable transmission apparatus according to the third aspect, the first power transmission path is formed by a first power transmission mechanism, the first power transmission mechanism including:
a first transmission shaft in parallel to the input shaft and the output shaft;
a first sprocket fixed to one end portion of the first transmission shaft;
a second sprocket fixed to the second disk being an output side disk;
a chain hung over between the first sprocket and the second sprocket; and
first and second gears meshed to each other and fixed to the other end portion of the first transmission shaft and the carrier, respectively.
Further, according to a fifth aspect of the invention, in the continuously variable transmission apparatus according to the third aspect, the second power transmission path is formed by a second transmission shaft disposed concentrically with the input shaft.
Moreover, according to a sixth aspect of the invention, in the continuously variable transmission apparatus according to the third aspect, the mode switching device is formed by a clutch mechanism, the clutch mechanism including:
a high speed clutch; and
a low speed clutch provided between an outer peripheral edge portion of the carrier and one end portion of the ring gear in axial direction thereof.
Additionally, according to a seventh aspect of the invention, in the continuously variable transmission apparatus according to the third aspect, the toroidal type continuously variable transmission is a double cavity type having a pair of input side disks and a pair of output side disks, and
wherein the first power transmission path is formed by a first power transmission mechanism, the first power transmission mechanism including:
a first transmission shaft in parallel to the input shaft and the output shaft;
a third gear fixed to one end potion of the first transmission shaft;
an output gear provided at an outer peripheral surface of an intermediate potion of an output sleeve engaged with both ends of the pair of output side disks;
a fourth gear supported by an outer peripheral surface of a sleeve rotatably disposed at periphery of an intermediate portion of the output shaft; and
a fifth gear fixedly provided at the other end portion of the first transmission shaft and meshed with the fourth gear through an idle gear.
Further, according to an eighth aspect of the invention, there is provided a continuously variable transmission apparatus comprising:
an input shaft coupled to a driving source and driven and rotated by the driving source;
an output shaft for taking out a power based on the rotation of the input shaft;
a toroidal type continuously variable transmission;
a planetary gear mechanism;
a first power transmission path for transmitting a power inputted into the input shaft through the toroidal type continuously variable transmission;
a second power transmission path for transmitting the power inputted into the input shaft without passing through the toroidal type continuously variable transmission; and
a mode switching device for switching a state where the power inputted into the input shaft is transmitted to the planetary gear mechanism through the first power transmission path and the second power transmission path,
wherein the toroidal type continuously variable transmission includes:
first and second disks each having a concave-shaped inner surface with an arc shape in section, the first and second disks being supported concentrically to be rotatable independently in a state that the inner surfaces thereof are opposed to each other;
a plurality of trunnions each swingably rotating around pivot shafts which are disposed at twisted positions with respect to a center shaft of the first and second disks;
displacement shafts each being supported by an intermediate portion of corresponding one of the trunnions in a state of protruding from an inner surface of the corresponding one of the trunnions;
power rollers each having a spherical convex-shaped periphery and disposed on an inner surface side of corresponding one of the trunnions, each of the power rollers being supported around a periphery of corresponding one of the displacement shafts to be rotatable in a state of being sandwiched between the first and second disks;
a pressing device which presses the first disk toward the second disk, the pressing device generating a first pressing force corresponding to a magnitude of a torque transmitted between the first and second disks and a second pressing force independent from the torque; and
a controller controlling the pressing device to generate the second pressing force in accordance with a signal, wherein, when a magnitude of a torque transmitted between the first and second disks varies, the controller controls the pressing device to continuously generate a predetermined pressing force equal to or more than a pressing force necessary for transmitting a larger torque before and after the variation during the variation,
wherein the planetary gear mechanism includes:
a sun gear;
a ring gear disposed at periphery of the sun gear;
a planetary gear provided between the sun gear and the ring gear; and
a carrier for rotatably supporting the planetary gear,
wherein a power transmitted through the first power transmission path and a power transmitted through the second power transmission path is freely transmitted to two of the sun gear, the ring gear and the carrier,
wherein the mode switching device switches between a mode for transmitting power at a low speed and a mode for transmitting power at a high speed, and
wherein the controller of the toroidal type continuously variable transmission controls the pressing device, during the switching of the mode switching device between the mode for transmitting power at a low speed and the mode for transmitting power at a high speed, to continuously generate a predetermined pressing force equal to or more than a pressing force necessary for transmitting a larger torque before and after the switching.
In the case of implementing the invention, under such a condition that the variation width of a torque can be predicted when the torque changes abruptly, a pressing force corresponding to a larger torque is generated based on the prediction. For example, in the case of the continuously variable transmission apparatus as described above, at the time of switching the clutch between the first mode and the second mode (low speed high speed), the magnitude of a torque applied to the toroidal type continuously variable transmission before and after the switching of the clutch can be predicted. Thus, in such a case, a suitable pressing force (a pressing force making it possible to transmit a larger torque) is generated from the pressing device based on the prediction according to signals of clutch switching and from an acceleration sensor etc. In contrast, when it is impossible to predict the torque variation in such cases of abrupt acceleration, an abrupt operation of an engine brake etc., it is realistic that the pressing device generates a pressing force (a pressing force capable of obtaining a contact pressure which makes it possible to transmit the maximum torque) corresponding to the maximum value of a torque (the maximum torque of an engine to be coupled) capable of being transmitted by the toroidal type continuously variable transmission. The reason is as follows. When the torque decreases abruptly, it is not necessarily required to generate a pressing force corresponding to the maximum torque so long as a pressing force corresponding to the torque just before the abrupt reduction of the torque. In contrast, when the torque increases abruptly, it cannot necessarily be predicted as to how the torque increases thereafter. When the engine brake is operated abruptly, although the transmission direction of the torque differs from the above case, also it can not necessarily be predicted as to how the torque increases thereafter. In order to effectively prevent the variation of the transmission ratio, it is necessary to increase the pressing force immediately by the controller in a state where the sign or indication of the torque variation is detected by the acceleration sensor etc. Thus, under a condition that the variation width of a torque can not be predicted, if the controller is arranged to have a function of generating a pressing force corresponding to the maximum torque immediately after the detection of the sensor for detecting the sign of the torque variation or the detection of the control resulting in the torque variation such as the switching of the clutch between the first mode and the second mode (low speed high speed) the variation of the transmission ratio can be prevented effectively. Of course, after the variation of the torque is converged, the controller returns to the normal control in which a pressing force corresponding to the torque to be transmitted is generated. The torque variation at the time of returning to the normal operation in this manner is known in the changing direction and the magnitude. Thus, it is easy to perform the control for suppressing the variation of the transmission ratio based on the torque variation at this time.
According to the toroidal type continuously variable transmission of the invention configured in the aforesaid manner, the variation of the transmission ratio at the time of the variation of the torque to be transmitted can be suppressed and the uncomfortable feeling applied to a driver can be reduced or eliminated.
That is, according to the toroidal type continuously variable transmission of the invention, even when the torque to be transmitted varies, the magnitude of a pressing force applied from the pressing device toward the first and second disks does not change. Thus, the variation of the transmission ratio based on the changes of the displacement amounts at the respective constituent portions based on the torque variation can be suppressed and so the unnecessarily change of the transmission ratio at the time of torque variation can be suppressed.